I. Technical Field
The present invention relates to a sound image localization control apparatus.
II. Description of the Related Art
Conventionally, when reproducing music, a movie or other contents in a vehicle, the sense of sound image localization is improved by adjusting gain balance or time alignment through delay insertion among speakers. With such a method, however, it is difficult to improve the sense of sound image localization at different seats with substantially the same degree. In order to solve this problem, an apparatus for erasing crosstalk among a plurality of speakers is proposed. Hereinafter, an audio reproduction apparatus described in Japanese Laid-Open Patent Publication No. 6-165298 will be described with reference to the figures.
FIG. 1 shows an audio reproduction apparatus described in Japanese Laid-Open Patent Publication No. 6-165298. In this figure, an audio reproduction apparatus 1 is applied to front seats of a vehicle. Specifically, two crew members L1 and L2 as listeners in the vehicle listen to a signal B1 reproduced by a recording device 2 with their left ears and to a signal B2 reproduced by the recording device with their right ears. Thus, both crew members perceive an audio effect of a content included in the recording device 2. In front of the crew members L1 and L2, four speakers 3a through 3d are provided, which are respectively connected to amplifiers 4a through 4d. Each set of a speaker and an amplifier forms audio generation means. The recording device 2 has audio information therein which is recorded by a known binaural recording system. The recording device 2 and the amplifiers 4a through 4d are connected to each other via an inverse filter network 5 constructed by the following procedure.
Before constructing the inverse filter network 5, an acoustic transfer function hij (i=1 through 4: subscript representing an ear; j=1 through 4: subscript representing a speaker) from each of the speakers 3a through 3d to each ear of each crew member is measured. The acoustic transfer functions other than h11, h21, h31 and h41 are not shown in the figure. FIG. 2 shows a method for measuring an acoustic transfer function hij. A test signal generation device 6 connected to the amplifiers 4a through 4d generates a wideband signal such as white noise or the like, and measures acoustic transfer functions hij using sounds S1 through S4 generated from the speakers 3a through 3d and sounds M1 through M4 measured at both ears of dummy heads D1 and D2 which are located at positions at which crew members are assumed to be sitting. In actuality, the speakers are driven sequentially. Namely, for example, while the speaker 3a is driven, the other speakers 3b through 3d are not driven. The generated sounds S1 through S4, the measured sounds M1 through M4, and the acoustic transfer functions fulfill the following relationships.
                    [                  Expression          ⁢                                          ⁢          1                ]                                                                      [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                              [                                                                                h                    11                                                                                        h                    12                                                                                        h                    13                                                                                        h                    14                                                                                                                    h                    21                                                                                        h                    22                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    32                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    42                                                                                        h                    43                                                                                        h                    44                                                                        ]                    ⁡                      [                                                                                S                    1                                                                                                                    S                    2                                                                                                                    S                    3                                                                                                                    S                    4                                                                        ]                                              (        1        )            
A target effect to be provided by the audio reproduction apparatus 1 is:
                    [                  Expression          ⁢                                          ⁢          2                ]                                                                      [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                              [                                                            1                                                  0                                                  0                                                  0                                                                              0                                                  1                                                  0                                                  0                                                                              0                                                  0                                                  1                                                  0                                                                              0                                                  0                                                  0                                                  1                                                      ]                    ⁡                      [                                                                                B                    1                                                                                                                    B                    2                                                                                                                    B                    1                                                                                                                    B                    2                                                                        ]                                              (        2        )            
Expression (2) can be modified into:
                    [                  Expression          ⁢                                          ⁢          3                ]                                                                      [                                                                      M                  1                                                                                                      M                  2                                                                                                      M                  3                                                                                                      M                  4                                                              ]                =                                                            [                                                                                                    h                        11                                                                                                            h                        12                                                                                                            h                        13                                                                                                            h                        14                                                                                                                                                h                        21                                                                                                            h                        22                                                                                                            h                        23                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        32                                                                                                            h                        33                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        42                                                                                                            h                        43                                                                                                            h                        44                                                                                            ]                            ⁡                              [                                                                                                    h                        11                                                                                                            h                        12                                                                                                            h                        13                                                                                                            h                        14                                                                                                                                                h                        21                                                                                                            h                        22                                                                                                            h                        23                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        32                                                                                                            h                        33                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        42                                                                                                            h                        43                                                                                                            h                        44                                                                                            ]                                                    -              1                                ⁡                      [                                                                                B                    1                                                                                                                    B                    2                                                                                                                    B                    1                                                                                                                    B                    2                                                                        ]                                              (        3        )            
The following Expressions are obtained by substituting expression (1) for expression (3).
                    [                  Expression          ⁢                                          ⁢          4                ]                                                                                  [                                                                                S                    1                                                                                                                    S                    2                                                                                                                    S                    3                                                                                                                    S                    4                                                                        ]                    =                                                    [                                                                                                    h                        11                                                                                                            h                        12                                                                                                            h                        13                                                                                                            h                        14                                                                                                                                                h                        21                                                                                                            h                        22                                                                                                            h                        23                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        32                                                                                                            h                        33                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        42                                                                                                            h                        43                                                                                                            h                        44                                                                                            ]                                            -                1                                      ⁡                          [                                                                                          B                      1                                                                                                                                  B                      2                                                                                                                                  B                      1                                                                                                                                  B                      2                                                                                  ]                                      ⁢                                                      (        4        )                                [                  Expression          ⁢                                          ⁢          5                ]                                                                                  [                                                                                h                    11                                                                                        h                    12                                                                                        h                    13                                                                                        h                    14                                                                                                                    h                    21                                                                                        h                    22                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    32                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    42                                                                                        h                    43                                                                                        h                    44                                                                        ]                                -            1                          =                              1                                        H                                              ⁡                      [                                                                                H                    11                                                                                        H                    21                                                                                        H                    31                                                                                        H                    41                                                                                                                    H                    12                                                                                        H                    22                                                                                        H                    32                                                                                        H                    42                                                                                                                    H                    13                                                                                        H                    23                                                                                        H                    33                                                                                        H                    43                                                                                                                    H                    14                                                                                        H                    24                                                                                        H                    34                                                                                        H                    44                                                                        ]                                                          
The inverse filter network 5 as shown in FIG. 1 is designed so as to fulfill expression (4) and provided in front of the amplifiers 4a through 4d. A signal for the left ear and a signal for the right ear are input to the inverse filter network 5 instead of an output from the test signal generation device 6. Then, the signals listened to by the left ear and the right ear of the dummy heads D1 and D2 are respectively a signal for the left ear and a signal for the right ear. It is assumed that in the inverse filter network 5 shown in FIG. 1, the signal for the left ear is input to an input section shown on a left part of the sheet of FIG. 1, and the signal for the right ear is input to an input section shown in a right part of the sheet of FIG. 1. Components included in the inverse filter network 5 are expressed by the following expressions.
                    ⁢                                        [                          Expression              ⁢                                                          ⁢              6                        ]                    ⁢                                                ⁢                            H                              =                                    h            11                    ⁡                      [                                                                                h                    22                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    32                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    42                                                                                        h                    43                                                                                        h                    44                                                                        ]                          -                              h            12                    ⁡                      [                                                                                h                    21                                                                                        h                    23                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    33                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    43                                                                                        h                    44                                                                        ]                          +                              h            13                    ⁡                      [                                                                                h                    21                                                                                        h                    22                                                                                        h                    24                                                                                                                    h                    31                                                                                        h                    32                                                                                        h                    34                                                                                                                    h                    41                                                                                        h                    42                                                                                        h                    44                                                                        ]                          -                                            h              14                        ⁡                          [                                                                                          h                      21                                                                                                  h                      22                                                                                                  h                      23                                                                                                                                  h                      31                                                                                                  h                      32                                                                                                  h                      33                                                                                                                                  h                      41                                                                                                  h                      42                                                                                                  h                      43                                                                                  ]                                ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            7                    ]                                        ⁢                  H        11            =              +                              {                                                            h                  22                                ⁡                                  [                                                                                                              h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                      ]                                            -                                                h                  23                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                      ]                                            +                                                h                  24                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            8                    ]                                        ⁢                  H        12            =              -                  {                                                    h                21                            ⁡                              [                                                                                                    h                        33                                                                                                            h                        34                                                                                                                                                h                        43                                                                                                            h                        44                                                                                            ]                                      -                                          h                23                            ⁡                              [                                                                                                    h                        31                                                                                                            h                        34                                                                                                                                                h                        41                                                                                                            h                        44                                                                                            ]                                      +                                          h                24                            ⁡                              [                                                                                                    h                        31                                                                                                            h                        33                                                                                                                                                h                        41                                                                                                            h                        43                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        9            ]                          ⁢                  H        13            =              +                              {                                                            h                  21                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                      ]                                            -                                                h                  22                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                      ]                                            +                                                h                  24                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            10                    ]                                        ⁢                  H        14            =              -                              {                                                            h                  21                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                      ]                                            -                                                h                  22                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          33                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                      ]                                            +                                                h                  23                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            11                    ]                                        ⁢                  H        21            =              -                              {                                                            h                  12                                ⁡                                  [                                                                                                              h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                      ]                                            -                                                h                  13                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                      ]                                            +                                                h                  14                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          33                                                                                                                                                              h                          42                                                                                                                      h                          43                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            12                    ]                                        ⁢                  H        22            =              +                              {                                                            h                  11                                ⁡                                  [                                                                                                              h                          33                                                                                                                      h                          34                                                                                                                                                              h                          43                                                                                                                      h                          44                                                                                                      ]                                            -                                                h                  13                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                      ]                                            +                                                h                  14                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          33                                                                                                                                                              h                          41                                                                                                                      h                          43                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            13                    ]                                        ⁢                  H        23            =              -                              {                                                            h                  11                                ⁡                                  [                                                                                                              h                          32                                                                                                                      h                          34                                                                                                                                                              h                          42                                                                                                                      h                          44                                                                                                      ]                                            -                                                h                  12                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          34                                                                                                                                                              h                          41                                                                                                                      h                          44                                                                                                      ]                                            +                                                h                  14                                ⁡                                  [                                                                                                              h                          31                                                                                                                      h                          32                                                                                                                                                              h                          41                                                                                                                      h                          42                                                                                                      ]                                                      }                    ⁢                                          ⁢                                          [                      Expression            ⁢                                                  ⁢            14                    ]                                        ⁢                  H        24            =              +                  {                                                    h                11                            ⁡                              [                                                                                                    h                        32                                                                                                            h                        33                                                                                                                                                h                        42                                                                                                            h                        43                                                                                            ]                                      -                                          h                12                            ⁡                              [                                                                                                    h                        31                                                                                                            h                        33                                                                                                                                                h                        41                                                                                                            h                        43                                                                                            ]                                      +                                          h                13                            ⁡                              [                                                                                                    h                        31                                                                                                            h                        32                                                                                                                                                h                        41                                                                                                            h                        42                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        15            ]                          ⁢                  H        31            =              +                  {                                                    h                12                            ⁡                              [                                                                                                    h                        23                                                                                                            h                        24                                                                                                                                                h                        43                                                                                                            h                        44                                                                                            ]                                      -                                          h                13                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        24                                                                                                                                                h                        42                                                                                                            h                        44                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        23                                                                                                                                                h                        42                                                                                                            h                        43                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        16            ]                          ⁢                  H        32            =              -                  {                                                    h                11                            ⁡                              [                                                                                                    h                        23                                                                                                            h                        24                                                                                                                                                h                        43                                                                                                            h                        44                                                                                            ]                                      -                                          h                13                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        24                                                                                                                                                h                        41                                                                                                            h                        44                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        23                                                                                                                                                h                        41                                                                                                            h                        43                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        17            ]                          ⁢                  H        33            =              +                  {                                                    h                11                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        24                                                                                                                                                h                        42                                                                                                            h                        44                                                                                            ]                                      -                                          h                12                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        24                                                                                                                                                h                        41                                                                                                            h                        44                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        22                                                                                                                                                h                        41                                                                                                            h                        42                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        18            ]                          ⁢                  H        34            =              -                  {                                                    h                11                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        23                                                                                                                                                h                        42                                                                                                            h                        43                                                                                            ]                                      -                                          h                12                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        23                                                                                                                                                h                        41                                                                                                            h                        43                                                                                            ]                                      +                                          h                13                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        22                                                                                                                                                h                        41                                                                                                            h                        42                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        19            ]                          ⁢                  H        41            =              -                  {                                                    h                12                            ⁡                              [                                                                                                    h                        23                                                                                                            h                        24                                                                                                                                                h                        33                                                                                                            h                        34                                                                                            ]                                      -                                          h                13                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        24                                                                                                                                                h                        32                                                                                                            h                        34                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        23                                                                                                                                                h                        32                                                                                                            h                        33                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        20            ]                          ⁢                  H        42            =              +                  {                                                    h                11                            ⁡                              [                                                                                                    h                        23                                                                                                            h                        24                                                                                                                                                h                        33                                                                                                            h                        34                                                                                            ]                                      -                                          h                13                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        34                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        23                                                                                                                                                h                        31                                                                                                            h                        33                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        21            ]                          ⁢                  H        43            =              -                  {                                                    h                11                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        24                                                                                                                                                h                        32                                                                                                            h                        34                                                                                            ]                                      -                                          h                12                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        24                                                                                                                                                h                        31                                                                                                            h                        34                                                                                            ]                                      +                                          h                14                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        22                                                                                                                                                h                        41                                                                                                            h                        32                                                                                            ]                                              }                                        ⁢          [              Expression        ⁢                                  ⁢        22            ]                          ⁢                  H        44            =              +                  {                                                    h                11                            ⁡                              [                                                                                                    h                        22                                                                                                            h                        23                                                                                                                                                h                        32                                                                                                            h                        33                                                                                            ]                                      -                                          h                12                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        23                                                                                                                                                h                        31                                                                                                            h                        33                                                                                            ]                                      +                                          h                13                            ⁡                              [                                                                                                    h                        21                                                                                                            h                        22                                                                                                                                                h                        31                                                                                                            h                        32                                                                                            ]                                              }                    
In the case where the signals B1 and B2 recorded by the binaural system are processed by the inverse filter network 5 constructed in this manner, the sound reaching the position of the left ear of the crew members L1 and L2 is of the signal B1, and the sound reaching the position of the right ear of the crew members L1 and L2 is of the signal B2. Therefore, both crew members can listen to the original sound field.
In the case where the structure shown in Japanese Laid-Open Patent Publication No. 6-165298 is provided with control means for processing an output from the recording device 2 with a digital filter or the like which simulates a predetermined acoustic transfer function and inputting the resultant signal to the inverse filter network 5, the sound image can be localized in a predetermined direction. FIG. 3 shows acoustic transfer functions G1 and G2 from a virtual sound source 7 to the left ear and the right ear of the dummy head D1. FIG. 4 shows an audio reproduction apparatus for localizing a sound image in a predetermined direction. In FIG. 4, elements equivalent to those in FIG. 1 bear identical reference numerals thereto. For filters 8a and 8b, predetermined acoustic transfer functions G1 and G2 are set as coefficients. As a sound source, a monaural sound source 9 having a monaural signal B0 recorded therein is used, not a sound recorded by the binaural system. In the structure shown in FIG. 4, the sounds at the positions of the left ear and the right ear of the crew members L1 and L2 are respectively G1•B0 and G2•B0 according to the above description. Therefore, the crew members L1 and L2 obtain a perception as if the sound was generated by the virtual sound source 7 shown in FIG. 3. The monaural signal B0 may be processed with the acoustic transfer functions G1 and G2 in advance, or the acoustic transfer functions G1 and G2 may be incorporated as elements of the inverse filter network 5. In these cases, substantially the same effect is provided.